U.S. Pat. No. 4,371,025 discloses a radial tire having an annular reinforcing structure comprising at least two layers of steel monofilaments arranged on a carcass having a radius of curvature, on the meridian plane in the crown point, equal to or greater than 400 mm. The monofilaments preferably have a specific tensile strength of at least 2000 N/mm.sup.2, a modulus of elasticity of 205,000 N/mm.sup.2, an elongation of 1.4 percent for a stress equal to 100 percent of the tensile strength. This patent does not address the fatigue properties of the monofilament. Whereas tires have been manufactured with belt plies incorporating steel monofilaments exceeding the values listed in this patent, those tires using steel monofilaments falling below the required fatigue properties described herein miserably failed practical testing conditions.